This project is concerned with understanding extinction, the loss of learned performance that occurs when a Pavlovian signal or an instrumental action is repeatedly presented without its reinforcer. Extinction is a naturally-occurring process of behavior change, as well as a tool used in clinical treatments designed to eliminate unwanted thoughts, emotions, and behaviors in humans. Although it is tempting to assume that extinction erases the original learning, extinguished performance readily recovers, and several recovery effects (e.g., renewal, reinstatement, rapid reacquisition, spontaneous recovery, and resurgence) indicate that the original learning may be largely intact. In addition, because these effects can be interpreted as effects of changing the background or context, they suggest that extinction results from new inhibitory learning that is especially sensitive to the context in which it is learned. The goal of this project is to seek an integrated understanding of extinction as it is revealed in these and other response-recovery processes. It will focus especially on the extinction of instrumental (operant) learning, because principles of operant learning are crucial for understanding a range of behavior problems-such as smoking, drug abuse, and eating and overeating-in which voluntary contact with reinforces plays an essential role. The experiments will involve rats as subjects. One set will test new methods for reducing the renewal effect (in which extinguished behavior relapses when the context is changed after extinction) and resurgence (in which a behavior has been extinguished and replaced by a second behavior relapses when the replacement behavior is itself extinguished). Another set will examine ways to inhibit rapid reacquisition (in which an extinguished action rapidly spirals into relapse when action-reinforcer pairings are reintroduced) and test the effects of hunger as a contextual stimulus influencing relapse. A third set will analyze the extinction-enhancing effects of administering D-cycloserine (a partial agonist of a brain receptor that is thought to play a role in learning), as well as new hypotheses about how to enhance the generalization of extinction to new contexts. A fourth set will analyze the extinction of sequences or chains of behavior in which the subject must purchase (or procure) access to the reinforcer before she can consume (or take) it. The results will increase our understanding of extinction, a fundamental behavioral and clinical phenomenon, and develop new ways to help promote extinction learning so as to minimize lapse and relapse.